An equidistant polytope is a special equidistant set in the space
all of whose
boundary points have equal distances from two finite systems of points. Since one of the finite
systems of the given points is required to be in the interior of the convex hull of the other
one, we can speak about inner and outer focal points of the equidistant polytope. It is of
type
, where
is the number of the
outer focal points and
is the number of the inner focal points. The equidistancy is the generalization of
convexity because a convex polytope can be given as an equidistant polytope of type
, where
. We
present some general results about the basic properties of the equidistant polytopes:
convex components, graph representations, connectedness, correspondence to the Voronoi
decomposition of the space etc. In particular, we are interested in equidistant polytopes of
dimension
(equidistant polygons). Equidistant polygons of
type
will be characterized in terms of a constructive (ruler-and-compass) process to
recognize them. In general they are pentagons with exactly two concave angles such
that the vertices at which the concave angles appear are joined by an inner diagonal
related to the adjacent sides of the polygon in a special way via the three reflections
theorem for concurrent lines. The last section is devoted to some special arrangements
of the focal points to get the concave quadrangles as equidistant polygons of
type .